1998 Chevy Silverado shifting

DRILLER

MEMBER
1998 CHEVROLET SILVERADO
V8
4WD
AUTOMATIC
170,000 MILES

This is a diesel pick up it has a 6.5 liter diesel I dont know what type of tranny. Here about a week ago it started shifing funny while driving about 50 mph then it started doing to at any speed above 45 it down shifts then up shifts and sometimes a bunch then sometimes not at all I had the fluid and filter changed didnt figure I had much to loose. I drove almost 300 miles yesterday and it only happen a couple times today I drove 50 miles and it happened alot any suggestions would help thank you

4 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

Have the PCM scanned for codes. If it picked up any failures it will have stored sometyhing that could lead us in the right direction. Does the speedo work ok while it is up and down shifting?

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Thursday, January 31st, 2008 AT 11:44 AM

DRILLER

MEMBER
2 POSTS

Yes thats whats confusing the speedometer works all the time. When I the truck has always shifted great the tachometer is the best way to tell when it is shifting up and down for the last week it has only done it when I first drive it just about ten miles then it doesnt do it anymore. Its got me confused

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Friday, February 1st, 2008 AT 8:15 AM

2CARPRO JACK

MECHANIC
11,533 POSTS

OD trans. Sounds like it is going in and out of OD, might have a bad Throttle sensor or something to that effect. Might need to go to a trans shop and have htem drive it. If something is wrong you dont want to damage the trans any further

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Friday, February 1st, 2008 AT 9:37 AM

INDYUKE

MECHANIC
416 POSTS

I agree with Jack. It either sounds like it going in and out of OD, or the torque converter lockup is cycling on and off for some reason.

If it's the OD, you can generally see a rpm change of about 500-800rpm, if it's the torque converter you'll see changes of about 200rpm or so when it happens.

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Friday, February 1st, 2008 AT 6:01 PM